1. Field of the Invention
This invention relates to a method of producing a screen for printing a heating line pattern and a method of forming a heating line pattern on a glass plate suitable for making an anti-fogging windshield.
2. Discussion of the Related Art
As a windshield which is fixed to a rear window frame or the like of an automobile, an anti-fogging windshield having an anti-fogging function to secure a safety view, has much been used.
In the anti-fogging windshield of this case, conventionally, an electrically conductive paste in a pertinent heating line pattern, is printed and sintered, which forms a heating line composed of bus bars and heating lines. The heating line generates heat by flowing electric current in it, by which a surface of the windshield is heated, and which performs defogging and anti-fogging.
In case of the above anti-fogging windshield, depending on a pattern of the heating line formed, the temperature of the surrounding area of an allocated part of an electricity feeding terminal in the bus bar is abnormally elevated in flowing electric current.
This is because, since the bus bar is formed by printing of the paste with uniform thickness near the electricity feeding terminal as well as the other part, much electric current is flown at the bus bar portion in electric heating and especially heat generation quantity near the electricity feeding terminal is increased compared with the other portion.
Therefore, conventionally, a copper plate is stuck at the surrounding area of the electricity feeding terminal in the bus bar, or the paste is multiple-coated, so that the thickness of the bus bar near the electricity feeding terminal is increased, and so that the resistance value of the surrounding area of the electricity feeding terminal is decreased, as a measure to prevent the excessive heat generation.
However, such copper sticking operation or an operation of multiple-coating of the paste, causes the complexity of the production process of the anti-fogging windshield, which not only lowers the operational efficiency, but also increases the production cost.
Moreover, when the thickness of the bus bar near the electricity feeding terminal is the same as that of the other portion, the strength of the soldering of the electricity feeding terminal on the bus bar becomes weak. As the result, the soldered terminal may break off.
As a measure for this problem, it may be considered that the thickness of the paste itself printed through the screen is increased, by increasing the thickness of the screen per se in the screen.
However, in resorting to these measures, the resistance value of the heating lines is also decreased. As a result, much electric power is required to sufficiently heat the heating lines, which causes increase of the power consumption and is not practical.